Human sphingosine kinase: molecular cloning, functional characterization and tissue distribution

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Signaling

Background:

• Sphingosine-1-phosphate (S1P) is a crucial signaling lipid involved in various cellular processes.
• The cloning of mouse sphingosine kinase prompted the investigation of its human counterpart.

Purpose of the Study:

• To clone, express, and characterize the human sphingosine kinase 1 (huSPHK1).
• To understand the evolutionary conservation and substrate specificity of huSPHK1.
• To investigate the expression patterns of huSPHK1 in various human tissues.

Main Methods:

• Gene cloning and expression of human sphingosine kinase 1 (huSPHK1).
• Enzyme kinetics assays to determine substrate specificity and inhibition constants.
• Northern blot analysis and database searches to assess tissue-specific expression.

Main Results:

• Human sphingosine kinase 1 (huSPHK1) exhibits high homology with murine sphingosine kinase and conserved regions across species.
• huSPHK1 specifically phosphorylates D-erythro-sphingosine and D, L-erythro-dihydrosphingosine, with Michaelis-Menten kinetics (Vmax=56µM, Km=5µM).
• The enzyme is inhibited by D,L-threo-dihydrosphingosine and N,N-dimethyl-sphingosine.
• Highest huSPHK1 expression is observed in adult lung and spleen, with notable presence in leukocytes, thymus, kidney, brain, and heart.
• huSPHK1 is also expressed in endothelial cells, retinal pigment epithelium, and senescent fibroblasts.

Conclusions:

• Human sphingosine kinase 1 (huSPHK1) is a highly conserved enzyme with specific substrate preferences.
• The expression profile suggests diverse roles for huSPHK1 in various human tissues and cell types.
• Understanding huSPHK1 function is critical for deciphering sphingolipid metabolism and signaling pathways.